fix(MCP): 重构MCPClient为后台协程 + AsyncExitStack管理，解决进程退出时的“Attempted to exit cancel scope in a different task”错误

# 变更
----
- 将所有stdio_client与ClientSession的创建/销毁都放到同一个后台 task 中
- 使用AsyncExitStack托管异步资源，cleanup时在同一task内执行exit_stack.aclose()
- 外部只通过事件通知后台task退出，避免跨协程调用cancel-scope异常

main/xiaozhi-server/core/mcp/manager.py

@@ -1,5 +1,5 @@
 """MCP服务管理器"""
-
+import asyncio
 import os, json
 from typing import Dict, Any, List
 from .MCPClient import MCPClient
@@ -94,8 +94,8 @@ class MCPManager:
         """
         for tool in self.tools:
             if (
-                tool.get("function") != None
-                and tool["function"].get("name") == tool_name
+                    tool.get("function") != None
+                    and tool["function"].get("name") == tool_name
             ):
                 return True
         return False
@@ -120,12 +120,13 @@ class MCPManager:
         raise ValueError(f"Tool {tool_name} not found in any MCP server")
 
     async def cleanup_all(self) -> None:
-        for name, client in self.client.items():
+        """依次关闭所有 MCPClient，不让异常阻断整体流程。"""
+        for name, client in list(self.client.items()):
             try:
-                await client.cleanup()
-                self.logger.bind(tag=TAG).info(f"Cleaned up MCP client: {name}")
-            except Exception as e:
+                await asyncio.wait_for(client.cleanup(), timeout=20)
+                self.logger.bind(tag=TAG).info(f"MCP client closed: {name}")
+            except (asyncio.TimeoutError, Exception) as e:
                 self.logger.bind(tag=TAG).error(
-                    f"Error cleaning up MCP client {name}: {e}"
+                    f"Error closing MCP client {name}: {e}"
                 )
         self.client.clear()